Fig. 1: Inhibition of the proliferation and overall EGFR kinase activity by ATO in NSCLC cell lines.

NCI-H1975, HCC827, and A549 cells were treated with ATO or gefitinib (g) for the indicated time. a Half maximal inhibitory concentrations (IC50) of arsenic and gefitinib in the three NSCLC cells were determined using CCK-8 for 48 h. The IC50 values of arsenic in NCI-H1975 were 2 µM and >8 µM in HCC827 and A549. The IC50 values of gefitinib were 0.01 µM in HCC827 and 10 µM in NCI-H1975 and A549. Black dotted line represents the IC50 concentration. **p < 0.0001 when compared with NCI-H1975 cells treated with arsenic. b EGFR tyrosine kinase activity was assayed when the cells were treated for 48 h using the assay kit and was calibrated based on the commercially purified EGFR WT. The OD450 (1.0) reached by 150 ng of EGFR WT was defined as one activity unit in this study. Arbitrary unit (AU) was used to represent the calibrated kinase activity (CKA), which was used to evaluate the kinase activity of the same quantity. Initial amount of EGFR for analysis in each group was 10 µg. *p < 0.05 when compared with A549 cells. c, a the NCI-H1975, HCC827, and A549 cells were treated with 2 µM of ATO at 24 and 48 h, and the expression levels of EGFR were detected by western blot analysis. b the CHO cells were transfected with the WT or mutant EGFR (ΔE746-A750 (ΔE-A) and L858R/T79M (L/T)), as well as the pEGFP-C1 blank vector. After 48 h of transfection, the GFP positive cells were purified by using cell sorter (BD FACSAria III). The sorted cells were seeded into the 24-well plates and treated with 2 µM of ATO for 48 h. The expression levels of EGFR were detected by western blot. The relative intensity was calculated according to the gray values of EGFR over that of β-actin or GAPDH with the Quantity One software. d Inhibitory rate of the overall EGFR activity was calculated using the following formula: inhibition rate = 1–EGFR overall activity after A or G treatment/EGFR overall activity before treatment. EGFR overall activity = CKA × quantity of EGFR. Original data were obtained from Fig. 1b, c and Tables S2, S3. Black dotted line indicates effective inhibitory level